This application claims priority of No. 097146106 filed in Taiwan R.O.C. on Nov. 28, 2008 under 35 USC 119, the entire content of which is hereby incorporated by reference.
1. Field of Invention
The present invention relates to the technology of optical storage media, and more particularly to a method for detecting a blank area of a power calibration area.
2. Related Art
In the present recording technology, an optimum power calibration (OPC) procedure is performed before recording in order to reduce the recording failure and increase the stability of the recorded data. Performing an optimum power control procedure can find a set of optimum laser powers suitable for the recording of this optical disc so that the jitter value or the decode error rate value of the radio frequency (RF) data recorded on the optical disc is better suppressed and the optimum write quality can be obtained.
However, the positions on the optical disc where the optimum power control procedure can be performed are specified in the specification of each optical disc, and not all the positions are suitable for the optimum power control procedure. The recordable optical disc, such as CD-R, DVD+R, DVD-R, or the like, only can be recorded once. If the optimum power control procedure is performed in the data area, then the formal data cannot be correctly recorded. The rewriteable optical disc, such as CD-RW, DVD+RW, DVD-RW, DVD RAM, or the like, can be recorded repeatedly. However, the recording time is significantly lengthened if the optimum power control procedure has to be performed in the data area in each recording procedure. Although the optical discs have various specifications, the specified area for the optimum power calibration procedure, which is referred to as a power calibration area (PCA), may be distributed in a lead-in area and a lead-out area (i.e., an innermost ring and an outermost ring of the optical disc).
The optimum power control procedure defined in the typical specification includes a β method mainly applied to the one-time programmable optical disc, and a γ method mainly applied to the rewriteable optical disc. The principles of the β and γ methods will be described in the following.
FIGS. 1A to 1C respectively show waveforms of three different radio frequency signals obtained after data is recorded with three different laser powers and then read back. As shown in FIGS. 1A to 1C, different powers of laser beams cause different depths of radio frequency signals, wherein the influence on the shorter radio frequency signal (e.g., 3T) is especially obvious. In the β method, different powers of laser beams are utilized to record the test data into the power calibration area, and then the optimum write power (Pwo) of the laser beam is searched according to the symmetry of the radio frequency signal. In the specification, the definition of β=(A1+A2)/(A1−A2) is also simultaneously made. So, when the β value approximates to zero, the radio frequency signal becomes the most symmetrical. That is, the jitter value or the decode error rate value is the minimum. As shown in FIG. 1A, |A1|<|A2| and β<0, which represent that the used laser power P is lower than the optimum write power Pwo. In FIG. 1B, |A1|≈|A2| and β≈0, which represents that the used laser power P is substantially equal to the optimum write power Pwo. In FIG. 1C, |A1|>|A2| and β>0, which represents that the used laser power P is higher than the optimum write power Pwo.
The γ method is similar to the β method in the write power, but the measurement and the calculation of the γ method are more complicated. FIGS. 2A and 2B are schematic illustrations showing the γ method used to define an optimum power. As shown in FIGS. 2A and 2B, M is firstly defined as the modulation amplitude according to the following equation:M=I14/I14H   EQ1
In addition, γ is defined as follows:
                    γ        =                                            ⅆ              m                                      ⅆ                              P                w                                              ×                                    P              w                        m                                              EQ        ⁢                                  ⁢        2            
Next, as shown in FIG. 2B, in which the relationship between γ and the write power is depicted, the optimum write power is determined according to the following equation:Ptarget=PW (power at γtarget).
PWO=ρ×Ptarget, wherein PWO is the optimum write power and ρ is the multiplication factor.
PEO=ε×PWO, wherein PEO is the optimum erase power, ε is a ratio of the erase power to the write power, and the values of γtarget, ρ and ε may be obtained by reading the absolute time in pre-groove (ATIP) in the lead-in area.
FIG. 3 is a schematic illustration showing a conventional optimum power calibration procedure. Referring to FIG. 3, the optimum power calibration procedure substantially includes the following steps.
In the first step, some parameters, such as βtarget, γtarget, and the like are obtained from the ATIP in the lead-in area of the optical disc, and the range of the laser power for test recording is calculated.
In the second step, a random EFM (Eight to Fourteen Modulation) signal is generated, and the test recording is performed in the power calibration area (PCA) of the lead-in area with 15 stages of test recording power P01 to P15 shown in the drawing.
In the third step, the random EFM signal recorded in the power calibration area is read back, and the optimum write power PWO is calculated according to the β (one-time programmable optical disc) or γ (rewriteable optical disc) method. In FIG. 3, the β method will be described as an example.
In the fourth step, the procedure of the optimum power calibration procedure ends.
In the present CD recording technology, the multi-time recording has been used. Thus, when the disc still has the unrecorded blank area and the disc is not finalized, the recording still can be continued. Thus, the optimum power calibration procedure still has to be performed on the disc. When the second time of optimum power calibration procedure is performed, it is necessary to search a blank area again in the lead-in area or the lead-out area to serve as the new power calibration area, and the above-mentioned four steps are performed in this new power calibration area. However, two drawbacks tend to be encountered when the second time of optimum power calibration procedure is performed.
First, the servo state is poor in the previous optimum power calibration and optimum focus position calibration procedures, the applied power is too small or the focus position deviates from the optimum focus point. Thus, the generated radio frequency signal is poor, or the amplitude of the radio frequency signal is too small. So, when the blank area detection (blank detection) is being performed, the recorded area (the area after the optimum power calibration procedure is performed) tends to be misjudged as the blank area.
Second, because the performance or the designed parameters of the blank area detection circuit are poor, the recorded area (the area after the optimum power calibration procedure is performed) tends to be misjudged as the blank area.
According to the first and second drawbacks, it is obtained that if the recorded area is misjudged as the blank area, the recorded area will be repeatedly recorded when the optimum power calibration procedure and the optimum focus position calibration procedure are subsequently performed. Thus, the results obtained after the optimum power calibration procedure and the optimum focus position calibration procedure are performed deviate from the expected results, or the calibration procedure may fail to cause the poor recording power or the poor focus position used in recording the data area. Finally, the recorded quality is poor or the recorded data cannot be easily read back. Consequently, it is obtained that the correctness of the blank area detection closely relates to the optimum power calibration procedure and the optimum focus position calibration procedure, so the correct and stable blank area detection becomes relatively important.